The invention relates to a hermetic electronic or optoelectronic package designed to receive electronic components and/or circuits.
The invention also relates to at least one process for manufacturing this package.
Optoelectronic components are used as converter, between an optical signal and an electrical signal or as converter between an electrical signal and an optical signal, or else are used as repeater on cables or optical fibres in order firstly to receive, amplify and then reinject a light signal. The development of 1.3 .mu.m laser heads for short-haul and medium-haul optical fiber links still requires the development of higher-performance packages for encapsulating these heads.
The development of other components not confined to optoelectronics also requires the production of reliable hermetic packages.
The two packages most commonly used, especially used for laser heads are, on the one hand, the DIL (Dual In-Line) package, because of the two lines of connection pins, and, on the other hand, the butterfly package, because the pins project out flat on each side of the package. An optoelectronic package has a rectangular parallelepipedal shape and comprises a bottom and a rectangular frame of variable height forming the side walls, of which:
one is the input wall in which a tubular opening is provided, which wall includes a guide tube for inserting the optical fibers and then for passing them into the package; PA1 a second wall, possibly also with a tubular opening for the emission of an optical signal; and PA1 at least one of the other remaining walls is provided with input and/or output means for conveying electrical signals, means on which pins are fastening allowing to establish the desired connections with a printed-circuit board. PA1 a metal baseplate serving as bottom; PA1 a first metal frame, fastened by brazing to this bottom; PA1 one of the side walls of which, called the input wall, includes a tubular opening and its associated tube for the passage of optical fibers; and PA1 the two opposed side walls of which, perpendicular to this input wall, are each cut back by a recess or indentation having a shape similar to a mortise and intended for placing the ceramic multilayer inserts; and PA1 a second metal frame fastened to the first frame by brazing, forming, by covering the recesses, slots into which these inserts are settled. PA1 a bottom formed from several superposed ceramic layers; and PA1 a frame forming side walls, this frame consisting of a stack of fashioned ceramic layers, each layer being shaped according to the function that it has and to the result that it must provide when it is combined with the other layers.
Among the most recent optoelectronic packages, there is a first generation of 14-pin butterfly packages. These are usually made of metal and are fitted with electrical-signal input/output means in the form of ceramic multilayer inserts or of connections through a glass bead via a glass-to-metal seal.
For example, a 2.times.7-pin package is known, which is composed, examining it from the bottom towards its lid, of:
This type of package, easily produced on an assembly line, even automated, is relatively bulky, heavy and expensive, because of the number of components used, and has the other drawbacks mentioned below. For example, when the diameter of the hole to be produced in the frame intended for the tubular opening increases, the height of the first frame must increase in relation to the diameter of the hole and, consequently, the achievement of the package becomes more expensive to produce because it is more complex. The implementation of two frames to achieve the package requires an additional brazing bond plane which entails an additional risk of hermeticity loss of the package. In addition, the connection pins project out flat in a plane parallel to the plane defined by the bottom or by the lid of the package.
However, the trend in electronic components and in emission-reception modules for optical fibers is towards the creation of more and more compact packages. These packages have a reduced volume and may, for example, comprise a restricted number of pins so as to reduce the cost of production, but also the weight and the overall volume. There is thus a second generation of 8-pin packages called mini-DIL or SiV package, the surface area ratio of which, with respect to the first generation, is about 0.33. These second-generation optoelectronic packages are generally of the ceramic type. They are compatible, pin to pin, with those of the 14-pin first generation, i.e. they can replace them without requiring to review the general design of the internal components. They are used in particular for laser chips that are highly temperature-stable and consequently do not have built-in Peltier coolers.
For example, a 2.times.4-pin mini-DIL package is known which, examining it from the bottom towards its lid, is composed of:
Thus, the stack of fashioned and shaped ceramic layers leads to the creation of side walls of the package. One of the walls, called the input wall, includes an orifice which forms a tunnel obtained by this stack and allows the optical fibers to be connected to the internal part of the package. Two other opposed walls, those perpendicular to the input wall, comprise, in their massive structure, the means for conveying the electrical signals, means on which pins for the connection are fastening. Placed above the stack of ceramic layers forming the bottom and the side walls of package is a metal frame for hermetically closing the package by means of a lid.
However, this more compact type of package has drawbacks that it is important to emphasize. For example, the change in diameter required for the passage of the optical fibers needs the design (thickness, etc.) of certain ceramic layers to be reconsidered so that the functions that they provide lead to the results expected from the stack of the various recessed layers. These dimensional changes are clearly expensive, because of the extensive new modeling that they require. The formation of a package, by stacking ceramic layers, particularly in the region of the tunnel-forming orifice, imposes that the various ceramic layers intended for forming the frame by stacking have non-recessed regions in order to give sufficient mechanical strength. The regions of good mechanical strength create an unnecessary increase in the package volume. The shielding against electromagnetic phenomena may prove to be insufficient when the package is subjected to high frequencies. Finally, the hermetic closing of the package may not be reliably accomplished using any method: the most suitable method is brazing, but the necessary rise in temperature introduces additional stresses in regard to the electronic components and/or circuits present in the package.
EP-A-514,213 describes two methods for achieving a package. In the first method, a strip is cut from a metal sheet. Folding regions are marked, or slightly notched, and openings or recesses are produced, which openings or recesses will be for means for conveying the optical or electrical transmission signals. Next, the strip is folded up on itself and then welded in order to form the final frame. Lastly, the frame is fastened to the bottom. In the second of the methods, the general and complete shape of the package is cut from a metal sheet. Folding regions are marked, or slightly notched, and openings or recesses are produced, which openings or recesses will be for means for conveying the optical or electrical transmission signals. Next, the strip and the bottom are folded up on themselves and then welded in order to form the final complete package.
The major drawbacks of these methods reside in the presence of folding regions and in the presence of welded faces or intersecting edges which affect the mechanical strength of the frame and the package. The presence of a flush weld bead may be a problem when resealing, by brazing, the package with the lid. In addition, accurate folding, adjusting and welding must be difficult to achieve.
U.S. Pat. No. 4,930,857 describes an electronic and optoelectronic metal package with a ceramic multilayer component. The frame includes, in its base, a rectangular indent for passage of a ceramic multilayer component. This component, with, moreover, the entire associated electronics, is placed directly on the bottom of the package and the frame fits onto the bottom, thus enclosing the component.
A major drawback of this type of package arrangement is that, although the frame is annular and made integral, the component remains placed on the bottom and all the electronic part, especially its conducting tracks and its electrical contacts, must fit in with the height, which is always constant, fixed in advance by the indent for this component. Another drawback is that the planarity of the frame will be difficult to obtain when brazing it to the bottom. Such deformations will result in a lack of hermeticity between the frame and the ceramic component or between the ceramic component and the bottom.